The present invention relates to the manufacturing of curved, for example cup-shaped, wall portions of heat insulating walls for insulating containers with curved surfaces, particularly for transportation and storage of liquids. More particularly, the present invention relates to a manufacturing of wall portions of heat insulating walls which include a heat insulating layer of synthetic foam material and a baffle layer, for example, a gas-tight layer, constituted of aluminum. The present invention also relates to an arrangement for manufacturing curved wall portions of the above-mentioned heat insulating walls.
Methods and arrangements for manufacturing such wall portions are known in the art. One known method of manufacturing a heat insulating wall for containers for transporting and storing liquids and gases includes the steps of forming a curved part of the insulating wall in a mold by foaming, applying a baffle layer formed as an aluminum foil onto the foam part and glueing the former to the latter in the correspondingly shaped mold, and mounting the thus-produced insulating wall on the container. This solution is, however, not satisfactory inasmuch as a plurality of the molds must be provided which considerably increases the cost of the container.
For avoiding the non-economically high mold costs, another method was proposed in the German Auslegeschrift No. 2,205,965. In accordance with the disclosed method, a flat part is cut from a plate of synthetic foam material and coated with an aluminum sheet which has the same contour and is provided with grain, grating, or wrinkle structures. The thus-cut portion coated with the aluminum sheet is pressed under the action of mass pressure in a curved (cup-shaped) mold with a curvature greater than the desired curvature of the wall part to be produced. The curved (cup-shaped) mold must be so stabilized that the aluminum foil having the grain, grating or wrinkle structure retains during closing of the press remaining elongation properties, and the profiling of the aluminum foil leads to straightening of the same. This method also possesses several disadvantages. During opening of the press, the curvature of the cut portion of the plate reduces to a certain extent, whereas during closing of the press not only the outer side of the cut portion with the aluminum foil is elongated, but also the inner side of the cut portion is compressed. The compressed inner side is not fixed in this condition, whereby during opening of the press a certain spring back takes place. The value of the spring back of the cut portion can be determined approximately only from experiments. This means that the accuracy of dimensions in the sense of the radius of curvature cannot be maintained within the required tolerances, and this problem aggravates with the reduction of the radius. It has been recognized that this method is applicable only for very great radii. Finally, in this method each radius of the wall portion requires provisions of a respective mold.
Both above-described methods possess the disadvantage in the fact that the joining edges of the wall portions do not exactly abut against one another. A wedge-shaped gap having greater or smaller width takes place, and it must be filled with a glue serving exclusively for lateral connection of the wall portions with one another. The utilization of expensive glue because of the non-uniformity of the edges of the wall portions can require several tons of glue for insulating such objects as tanks of large liquid fuel tankers.
Also, methods and arrangements for manufacturing a curved blank is disclosed in U.S. Pat. Nos. 3,491,631; 3,850,061; 4,111,085; DE-OS No. 1,906,502; DE-OS No. 2,849,254. The methods and arrangements disclosed in these patents have disadvantages in the sense that they cannot produce a curved blank with exact curvature of the spherical surface of the curved blank.